Top 50 Node.js Interview Questions and Answers | Edureka

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Node JS Interview
Questions
Differentiate between JavaScript
and NodeJS.
Question 1

Node JS Interview
Questions
Question 1
Differentiate between JavaScript
and NodeJS.
Type Programming Language
Interpreter and environment for
JavaScript
Utility
Used for any client-side activity for a
web application
Used for accessing or performing any
non-blocking operation of any
operating system
Running Engine
Spider monkey (FireFox), JavaScript
Core (Safari), V8 (Google Chrome), etc.
V8 (Google Chrome)

Node JS Interview
Questions
What Is Node.js?
Question 2

Node JS Interview
Questions
Question 2
What Is Node.js?
Powerful JavaScript
Framework
Developed on Chrome’s
V8 JavaScript engine
Compiles JavaScript
directly into the native
machine code
Used for creating server-
side web applications
Right pick for the data-intensive
real-time applications
</>
0110

Node JS Interview
Questions
List down the major benefits of
using Node.js?
Question 3

Node JS Interview
Questions
List down the major benefits of
using Node.js?
Question 3
Open Source Simple & Fast Asynchronous
High Scalability Single Threaded
No Buffering Cross Platform

Node JS Interview
Questions
What is the difference between
Angular and Node.js?
Question 4

Node JS Interview
Questions
Angular and Node.js?
Question 4
Open source web application development
framework
Cross-platform run-time environment for
applications
Written in TypeScript Written in C, C++ and JavaScript languages
Used for building single-page client-side
web applications
Used for building fast and scalable server-
side networking applications
Angular itself is a web application
framework
Node.js has many different frameworks like
Sails.js, Partial.js, and Express.js, etc.
Ideal for creating highly active and
interactive web apps
Ideal for developing small size
projects
Helpful in splitting an app into MVC
components
Helpful in generating database
queries
Suitable for developing real-time
applications
Suitable in situations where something
faster and more scalable is required

Node JS Interview
Questions
Why Node.js is single threaded?
Question 5

Node JS Interview
Questions
Question 5
Why Node.js is single threaded?
Node.js uses a single threaded model in order to support async processing
With async processing, an application can perform better and is more scalable
under web loads
Node.js makes use of a single-threaded model approach rather than typical
thread-based implementation

Node JS Interview
Questions
How do Node.js works?
Question 6

Node JS Interview
Questions
Node.js is a virtual machine that uses JavaScript as its scripting language and
runs on a v8 environment.
It works on a single-threaded event loop and a non-blocking I/O which
provides high rate as it can handle a higher number of concurrent requests.
By making use of the ‘HTTP’ module, Node.js can run on any stand-alone web
server.
How do Node.js works?
Question 6

Node JS Interview
Questions
Where Node.js can be used?
Question 7

Node JS Interview
Questions
Where Node.js can be used?
Question 7
Real-Time Web
Applications
Network
Applications
Distributed
Systems
General Purpose
Applications

Node JS Interview
Questions
How many types of API functions
are there in Node.js?
Question 8

Node JS Interview
Questions
How many types of API functions
are there in Node.js?
Question 8
Asynchronous, non-blocking functions
1
Synchronous, blocking functions
2

Node JS Interview
Questions
Asynchronous and Non-blocking?
Question 9

Node JS Interview
Questions
Asynchronous and Non-blocking?
Question 9 Asynchronous
Non-Blocking
Using these we can make asynchronous HTTP requests that do
not wait for the server to respond.
These functions continue to respond to the request for which it
has already received the server response.
Non-blocking functions are used in regards with I/O operations.
They immediately respond with whatever data is available and
keeps on running as per the requests.

Node JS Interview
Questions
What is package.json?
Question 10

Node JS Interview
Questions
What is package.json?
Question 10
The package.json file in Node.js is the heart of the entire application.
It is basically the manifest file that contains the metadata of the project where
we define the properties of a package.
{
"author": "Edureka",
"name": "Express_Demo",
"description": "Express with Node.js",
"version": "0.0.0",
"scripts": {
"start": "node script.js"
},
"engines": {
"node": "~0.4.12"
},
"dependencies": {
"connect-flash": "^0.1.1",
"cookie-parser": "^1.4.3",
"express": "^3.21.2",
"jade": "^0.20.3",
"req-flash": "0.0.3"
},
"devDependencies": {}
}

Node JS Interview
Questions
What do you understand by Event-
driven programming?
Question 11

Node JS Interview
Questions
Event-driven programming is a programming approach that heavily makes use
of events for triggering various functions.
What do you understand by Event-
driven programming?
Question 11
This approach mainly follows the publish-subscribe pattern.

Node JS Interview
Questions
What is an Event loop in Node.js
and how does it work?
Question 12

Node JS Interview
Questions
An event loop in Node.js handles all the asynchronous callbacks in an
application.
This approach mainly follows the publish-subscribe pattern.
What is an Event loop in Node.js
and how does it work?
Question 12

Node JS Interview
Questions
Explain REPL in the context of
Node.js
Question 13

Node JS Interview
Questions
Question 13
Explain REPL in the context of
Node.js
ead
val
rint
oop
Reads the user’s input, parses it into JavaScript data-
structure and then stores it in the memory.
Receives and evaluates the data structure
Prints the final result
Loops the provided command until CTRL+C is pressed
twice

Node JS Interview
Questions
List down the tasks which should
be done asynchronously using the
event loop?
Question 14

Node JS Interview
Questions
Question 14
List down the tasks which should
be done asynchronously using the
event loop?
Input Output
Operations
Heavy
Computations
Blocking
Operations

Node JS Interview
Questions
List down the steps using which
“Control Flow” controls the
function calls in Node.js?
Question 15

Node JS Interview
Questions
Question 15
List down the steps using which
“Control Flow” controls the
function calls in Node.js?
Control Order of
Execution
Collect Data
Limit Concurrency Invoke Next Step

Node JS Interview
Questions
What do you understand by a test
pyramid?
Question 16

Node JS Interview
Questions
Question 16
What do you understand by a test
pyramid?
`
End To End
`
Integration Tests
`
Unit Tests

Node JS Interview
Questions
What is an error-first callback in
Node.js?
Question 17

Node JS Interview
Questions
Question 17
What is an error-first callback in
Node.js?
var myPost = new Post({title: ‘edureka’});
myPost.save(function(err,myInstance){
if(err){
//handle error and return
}
//go ahead with `myInstance`
});

Node JS Interview
Questions
Explain the purpose of
module.exports?
Question 18

Node JS Interview
Questions
Question 18
Explain the purpose of
module.exports?
A module in Node.js is used to encapsulate all the related codes into
a single unit of code which can be interpreted by shifting all related
functions into a single file

Node JS Interview
Questions
What do you understand by
Reactor Pattern in Node.js?
Question 19

Node JS Interview
Questions
Question 19
Reactor Pattern in Node.js?
Reactor Pattern in Node.js is basically a concept of non-blocking I/O operations
This pattern provides a handler that is associated with each I/O operation
As soon as an I/O request is generated, it is then submitted to a demultiplexer
This demultiplexer is a notification interface which is capable of handling
concurrency in non-blocking I/O mode
It also helps in collecting each and every request in the form of an event and
then place each event in a queue
Thus resulting in the generation of the Event Queue

Node JS Interview
Questions
What’s the difference between
‘front-end’ and ‘back-end’
development?
Question 20

Node JS Interview
Questions
Question 20
What’s the difference between
‘front-end’ and ‘back-end’
development?
Front End
Development
Back End
Development
Uses mark up and web languages
like HTML, CSS, JavaScript
Uses programming and scripting
languages like Python, Ruby, Perl, etc.
Based on asynchronous requests
and AJAX
Based on Server Architecture
Better Accessibility Enhanced Security
Used for SEO Used for Backup

Node JS Interview
Questions
What are LTS releases of Node.js?
Question 21

Node JS Interview
Questions
Question 21
What are LTS releases of Node.js?
This version of Node.js receives all the critical bug fixes along with
security updates and performance improvements. It is supported for at
least 18 months and mainly focus on stability and security
ong erm upport

Node JS Interview
Questions
List down the major security
implementations within Node.js?
Question 22

Node JS Interview
Questions
Question 22
List down the major security
implementations within Node.js?
Authentication
Error Handling

Node JS Interview
Questions
callback hell?
Question 23

Node JS Interview
Questions
Question 23
callback hell?
01
02
03
Callback Hell is also known as
the Pyramid of Doom
It is a pattern caused by intensively nested
callbacks which are unreadable and unwieldy
It typically contains multiple nested callback functions which in
turn make the code hard to read and debug
async_A(function(){
async_B(function(){
async_C(function(){
async_D(function(){
....
});
});
});
});

Node JS Interview
Questions
Explain libuv.
Question 24

Full-featured event loop backed
Node JS Interview
Questions
Question 24
Libuv is a multi-platform support library of Node.js which majorly is used for
asynchronous I/O
Explain libuv.
File system events
Asynchronous file & file system operations
Asynchronous TCP & UDP sockets
Child processes

Node JS Interview
Questions
Explain the concept of middleware
in Node.js?
Question 25

Node JS Interview
Questions
Question 25
Middleware is a function receives the Request and Response objects
Explain the concept of middleware
in Node.js?
Execute any type of code
Update or modify the request and the response objects
Finish the request-response cycle
Invoke the next middleware in the stack
Commonly Performed Tasks

Node JS Interview
Questions
Explain the concept of URL module.
Question 26

Node JS Interview
Questions
Question 26
Explain the concept of URL module.
The URL module of Node.js provides various utilities
for URL resolution and parsing.
It is a built-in module that helps in splitting up the web
address into a readable format.
var url = require('url');
var adrs = 'http://localhost:8082/default.htm?year=2019&month=april';
var q = url.parse(adr, true);
console.log(q.host); //returns 'localhost:8082'
console.log(q.pathname); //returns '/default.htm'
console.log(q.search); //returns '?year=2019 and month=april'
var qdata = q.query; //returns an object: { year: 2019, month: 'april' }
console.log(qdata.month); //returns 'april'

Node JS Interview
Questions
What do you understand by ESLint?
Question 27

Node JS Interview
Questions
Question 27
What do you understand by ESLint?
ESLint is an open source project initially developed by Nicholas C. Zakas in 2013
It aims to provide a linting utility for JavaScript through a plug
Linters in Node.js are good tools for searching certain bug classes, especially
those which are related to the variable scope.

Node JS Interview
Questions
For Node.js, why Google uses V8
engine?
Question 28

Node JS Interview
Questions
Question 28
Google uses V8 as it is a Chrome runtime engine that converts JavaScript code
into native machine code
It speeds up the application execution and response process and give you a fast
running application.
For Node.js, why Google uses V8
engine?

Node JS Interview
Questions
Explain the working of the control
flow function.
Question 29

Node JS Interview
Questions
Question 29
The control flow function is basically the code that is executed between
the asynchronous function calls
Explain the working of the control
flow function.
The order of execution must be
controlled
1
The required data needs to be
collected
2
The concurrency must be limited3
The next step of the program
must be invoked
4

Node JS Interview
Questions
List down the two arguments that
async.queue takes as input?
Question 30

Node JS Interview
Questions
Question 30
List down the two arguments that
async.queue takes as input?
Task Function
Concurrency
Value

Node JS Interview
Questions
Differentiate between spawn() and
fork() methods in Node.js?
Question 31

Node JS Interview
Questions
Question 31
spawn()
fork()
Differentiate between spawn() and
fork() methods in Node.js?
It is a special instance of spawn() that
executes a new instance of the V8 engine.
The spawn() is used to launch a new process
with the provided set of commands.

Node JS Interview
Questions
What do you understand by global
objects in Node.js?
Question 32

Node JS Interview
Questions
What do you understand by global
objects in Node.js?
Question 32
Globals are the objects which are global in nature and are available in all the
modules of the application
You can use these objects directly in your application, rather than having to
include them explicitly
The Global objects can be modules, functions, strings, object, etc
Some of these objects can be in the module scope instead of Global Scope.

Node JS Interview
Questions
Explain the concept of stub in
Node.js.
Question 33

Node JS Interview
Questions
Explain the concept of stub in
Node.js.
Question 33
Stubs are basically the programs or functions that are used
for stimulating the module or component behavior
During any test cases, stubs provide the canned answers of
the functions

Node JS Interview
Questions
How assert works in Node.js?
Question 34

Node JS Interview
Questions
Question 34
How assert works in Node.js?
Assert is used to write tests
It only provides feedback only when any of the running
test cases fails
This module gives you a set of assertion tests which are then
used for testing invariants
It is basically used internally by Node.js but using require(‘assert’) code, it can be
used in other applications as well
var assert = require('assert');
function mul(a, b) {
return a * b;
}
var result = mul(1,2);
assert( result === 2, 'one multiplied by two is two');

Node JS Interview
Questions
Define the concept of the test
pyramid. Explain the process to
implement them in terms of HTTP
APIs.
Question 35

Node JS Interview
Questions
Define the concept of the test
pyramid. Explain the process to
implement them in terms of HTTP
APIs.
Question 35
01 The test pyramid is basically a concept that is developed by Mike Cohn
02
You should have a higher number of low-level unit tests as compared
to high-level end-to-end tests that running through a GUI.
03 In terms of HTTP APIs it may be defined as:
A higher number of low-level unit tests for each model
Lesser integration tests to test model interactions
Lesser acceptance tests for testing actual HTTP endpoints

Node JS Interview
Questions
Explain the purpose of ExpressJS
package?
Question 36

Node JS Interview
Questions Express.js is a framework built on top of Node.js that facilitates the
management of the flow of data between server and routes in the
server-side applications
If you are working with any of the connect based middleware modules,
then you can easily integrate with Express.js
Explain the purpose of ExpressJS
package?
Question 36
It is a lightweight and flexible framework that provides a wide range of features for
web applications
Express.js is developed on the middleware module of Node.js called connect

Node JS Interview
Questions
Differentiate between
process.nextTick() and
setImmediate()?
Question 37

Node JS Interview
Questions
process.nextTick() and setImmediate(), both are functions of the
Timers module which help in executing the code after a predefined period
Question 37
Differentiate between
process.nextTick() and
setImmediate()?
It waits for the execution of action till the next pass around
in the event loop or once the event loop is completed only
then it will invoke the callback function
It waits for the execution of action till the next pass around
in the event loop or once the event loop is completed only
then it will invoke the callback function
process.nextTick()
setImmediate()

Node JS Interview
Questions
Explain the usage of a buffer class in
Node.js?
Question 38

Node JS Interview
Questions
Buffer class in Node.js is used for storing the raw data in a similar manner of an array
of integers
Explain the usage of a buffer class in
Node.js?
Question 38
But it corresponds to a raw memory allocation that is located outside the V8 heap
It is a global class that is easily accessible can be accessed in an application without
importing a buffer module.
Buffer class is used because pure JavaScript is not compatible with binary data

Node JS Interview
Questions
How does Node.js handle the child
threads?
Question 39

Node JS Interview
Questions
How does Node.js handle the child
threads?
Question 39
Node.js is a single threaded process and doesn’t expose the child threads or
thread management methods
You can still make use of the child threads using spawn() for some specific
asynchronous I/O tasks
If you still want to use the threading concept in your application you have to
include a module called ChildProcess explicitly.

Node JS Interview
Questions
Explain stream in Node.js along with
its various types.
Question 40

Node JS Interview
Questions Streams in Node.js are the collection of data similar to arrays and strings. They are objects using
which you can read data from a source or write data to a destination in a continuous manner
Explain stream in Node.js along with
its various types.
Question 40
These streams are especially useful for reading and processing a
large set of data
04
01
02
03
Readable
Writable
Duplex
TransformIn Node.js, there are four fundamental types of streams:

Node JS Interview
Questions
What is the use of NODE_ENV?
Question 41

Node JS Interview
Questions
Question 41
What is the use of NODE_ENV?
NODE_ENV
If the project is in the production stage, Node.js promotes the convention of making use
of NODE_ENV variable to flag it
This helps in taking better judgment during the development of the projects
Setting your NODE_ENV to production, makes your application to perform 3 times faster

Node JS Interview
Questions
Differentiate between readFile vs
createReadStream in Node.js?
Question 42

Node JS Interview
Questions
readFile()
Differentiate between readFile vs
createReadStream in Node.js?
Question 42
createReadStream()
File System
Fully Buffered Process Partially Buffered Process
Returns the response only when the
complete file is pushed into the buffer and
is read
The entire file is split into chunks which are
then processed and sent back as a response
one by one
It is a memory intensive process It is a memory effective process

Node JS Interview
Questions
List down the various timing features
of Node.js.
Question 43

Node JS Interview
Questions
Question 43
setTimeout/clearTimeout
List down the various timing features
of Node.js.
setInterval/clearInterval
setImmediate/clearImmediate
process.nextTick

Node JS Interview
Questions
Explain the concept of Punycode in
Node.js?
Question 44

Node JS Interview
Questions
Explain the concept of Punycode in
Node.js?
Question 44
Punycode is an encoding syntax that is used for converting Unicode (UTF-8) string of
characters into a basic ASCII string of characters
It is important as the hostnames can only understand the ASCII characters
Node.js version 0.6.2 onwards, it was bundled up with the default Node package
punycode = require('punycode');

Node JS Interview
Questions
Differentiate between Node.js vs Ajax?
Question 45

Node JS Interview
Questions
Question 44
Differentiate between Node.js vs Ajax?
✓ Node.js is a server-side technology
✓ Required to develop the server software that are
typically executed by the servers instead of the
web browsers
✓ Ajax is client-side technology
✓ Required for updating or modifying the webpage
contents without having to refresh it

Node JS Interview
Questions
Does Node.js provide any Debugger?
Question 46

Node JS Interview
Questions
Node.js do provide a simple TCP based protocol and debugging
client that comes built-in.
Does Node.js provide any Debugger?
Question 46
node debug [script.js | -e "script" | <host> : <port> ]

Node JS Interview
Questions
Describe the exit codes of Node.js.
Question 47

Node JS Interview
Questions
The exit codes in Node.js are a set of specific codes which are
used for finishing a specific process.
Describe the exit codes of Node.js.
Question 47
Unused
Fatal Error
Uncaught fatal exception
Internal JavaScript Evaluation Failure
Internal Exception handler Run-time failure

Node JS Interview
Questions
What do you understand by an Event
Emitter in Node.js?
Question 48

Node JS Interview
Questions
EventEmitter is a Node.js class that includes all the objects that
are capable of emitting events.
What do you understand by an Event
Emitter in Node.js?
Question 48
const EventEmitter = require('events');
class MyEmitter extends EventEmitter { }
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');

Node JS Interview
Questions
Is cryptography supported in Node.js?
Question 49

Node JS Interview
Questions
Node.js does support cryptography through a module called Crypto.
This module provides various cryptographic functionalities like cipher,
decipher, sign and verify functions etc.
Is cryptography supported in Node.js?
Question 49
const crypto = require'crypto');
const secret = 'akerude';
const hash = crypto.createHmac('swaEdu',
secret).update('Welcome to Edureka').digest('hex');
console.log(hash);

Node JS Interview
Questions
Explain the reason as to why Express
‘app’ and ‘server’ must be kept
separate.
Question 50

Node JS Interview
Questions
Faster testing execution
It allows testing the API in-process without having to perform the
network calls
Better separation of concerns and cleaner
code
Getting wider coverage metrics of the code
Reasons for separating Express
‘app’ and ‘server’ separate
Allows deploying the same API under flexible and different network
conditions
Explain the reason as to why Express
‘app’ and ‘server’ must be kept
separate.
Question 50

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